(a) Fields of the Invention
The present invention relates to semiconductor devices including pads for bonding which are electrically continuous with Cu interconnects.
(b) Description of Related Art
In recent years, Cu wiring processes have been positively introduced for the purpose of attaining speed enhancement and miniaturization of semiconductor devices. In the case where a Cu pad for bonding is composed of part of Cu wiring, the top of the Cu pad is formed with an aluminum interconnect (Al pad). In this case, if copper contained in the Cu pad exudes into the Al pad, some troubles occur in which the Al pad corrodes or Al hardens due to impurity mixing (hardening caused by impurities). The Cu exudation will possibly have an adverse effect on the Al pad in process steps conducted on the Al pad, such as wafer test probing and wafer dicing after completion of a wafer process, and a wire bonding step and a package sealing step during package assembly.
Hereinafter, a conventional semiconductor device including a Cu pad and an Al pad (see, for example, Japanese Unexamined Patent Publication No. 2002-353221) will be described with reference to the accompanying drawings.
FIGS. 8A and 8B are sectional views showing main parts of the conventional semiconductor device. Referring to FIGS. 8A and 8B, the conventional semiconductor device includes: a copper connection via 111 embedded in an intermediate insulating film 108 on a silicon substrate 101; an Al pad 113 formed above the copper connection via 111 and embedded in a protective insulating film 115; and a barrier metal 112 of TaN formed between the Al pad 113 and the copper connection via 111. With such a structure, the barrier metal 112 blocks copper diffusion from the copper connection via 111 to prevent copper mixing into the Al pad and improve the bonding capability of the pad.
Another conventional semiconductor device includes a device in which a barrier metal serving as an adhesion layer or a diffusion inhibiting layer is provided between a Cu pad and an Al pad to prevent the reaction between copper and aluminum and oxidation of the Cu pad (see, for example, Japanese Unexamined Patent Publications Nos. 2001-15516, 2005-19493, and 2003-31575).